Many predications can be made about what will happen in the future. A common consensus is that energy usage will need to be more economical and efficient.
New technologies will be needed, for example, to enhance the electricity grid and thereby improve distribution of electricity to Germany’s cities. In particular, it will be necessary to operate such systems effectively.
In response to this possible need of the future, the industrial gases specialist Messer has developed a new cryogenic technology for the ‘AmpaCity’ project of the energy supplier RWE.
This makes it possible to use liquid nitrogen to cool superconducting cables down to -209°C. In the past it was only possible to cool the cables to -196°C. A difference of 13°C is enough to allow electricity to be transported through the grid almost lossless.
Due to this development, the ‘AmpaCity’ project has now qualified for ‘KlimaExpo.NRW’, an initiative from local government in North-Rhine Westphalia and Germany’s Federal Ministry for Economic Affairs and Energy.
As part of the pilot project, the longest superconducting cable ever commissioned went into action in Essen, Germany, in April 2014. In the long–term, superconducting cables should considerably reduce energy losses from electrical transmission lines. This is because superconducting cables can transport five times the amount of electricity through cables of the same cross-section and do so at a relatively low voltage. In addition, there will be savings on both cost and space for operators and communities.
Not without nitrogen
The energy loss occurring in present-day electrical transmission lines is based on electrical resistance to the transport of current. Some materials can lose their resistance entirely at very low temperatures and become superconductors. The (metallic) superconductors discovered about a century ago had to be cooled down to -269°C. This, however, requires costly helium refrigeration and high-energy consumption to run the cryogenic system.
Yet notably, in 1986, Nobel Prize winner Georg Bednorz discovered high-temperature superconductors, which can be cooled with liquid nitrogen rather than helium – and the transmission line used in the ‘AmpaCity’ project is made of this material.
Messer has developed a new refrigeration technology for this purpose with a cooling temperature of -209°C. Normally, it is not possible to cool anything to lower than -196°C using liquid nitrogen. However, Messer’s new cryogenic technology vaporises nitrogen at below atmospheric pressure, which allows a temperature of -209°C to be attained, thus achieving the specification for the cables.
It is not possible to reduce the temperature any further since nitrogen freezes at -210°C. At -209°C the refrigerated nitrogen compensates the heat absorbed by the ‘AmpaCity’ superconductor cable from the surroundings and makes it possible to transport electricity with almost no losses.
A reflux system allows an energy-efficient closed circuit.